The present invention relates to a joined body where a plurality of members to be joined are unitarily joined by means of a bonding material layer and a method for manufacturing the joined body.
A honeycomb structure is widely used as a trapping filter for exhaust gas, for example, a diesel particulate filter (DPF) for trapping and removing particulate matter contained in exhaust gas from a diesel engine or the like.
Such a honeycomb structure has a structure where a plurality of cells functioning as fluid passages partitioned and formed by porous partition walls of, for example, silicon carbide (SiC) are disposed in parallel with one another in the direction of the central axis. In addition, the end portions of adjacent cells are alternately plugged (in a checkerwise pattern). That is, one cell has an open end portion on one side and closed end portion on the other side, and other cells have a closed end portion on one side and an open end portion on the other side.
Such a structure enables exhaust gas to be purified by allowing the exhaust gas to flow into predetermined cells (inflow cells) from one end, to pass through porous partition walls, and to be discharged from the cells adjacent to the inflow cells (outflow cells) in order to trap particulate matter in exhaust gas with the partition walls when the exhaust gas passes through the partition walls.
In order to use such a honeycomb structure (filter) continuously for a long period of time, it is necessary to regularly subject the filter to a regeneration treatment. That is, in order to reduce a pressure loss increased by particulate matter accumulated in the filter with the passage of time to put the filtering performance in the initial state, it is required to remove the particulate matter accumulated in the filter by combustion. However, there is a problem of causing defects such as a crack or a rupture in a honeycomb structure due to large thermal stress which generates upon regeneration of a filter. In order to cope with the demand for improvement of thermal shock resistance against the thermal stress, there has been proposed a honeycomb structure having a divided structure having a function of dispersing and relaxing the thermal stress by unitarily joining a plurality of honeycomb segments with a bonding material layer. Thus, the thermal shock resistance could be improved to some extent.
However, a demand for further enlargement of a filter has been increasing in recent years, and thermal stress generated upon regeneration has been increasing according to this. Therefore, in order to solve the above problem, further improvement in thermal shock resistance as a structure has strongly been desired. In order to realize the movement in thermal shock resistance, a bonding material layer for unitarily joining a plurality of honeycomb segments is required to have excellent stress-relaxing function and bonding strength.
For the purpose of enhancing thermal shock resistance by such improvement of the bonding material layer, there has conventionally been disclosed a ceramic structure where a material for a bonding material layer between honeycomb segments has a Young's modulus of 20% or less with respect to that of a material for the honeycomb segments (JP-A-2001-190916). The honeycomb structure has the bonding material layer having low Young's modulus, thereby lowering thermal stress generated upon use. However, because of the low Young's modulus, bonding strength between honeycomb segments is insufficient when the bonding material layer has high porosity, and sometimes a sound joined body cannot be obtained.
In contrast with this, when the bonding material layer has high Young's modulus, deformation of the honeycomb segments due to thermal distortion can be suppressed by the bonding material layer. However, since it increases stress applied on the bonding material layer, there arises a problem that the bonding material layer is prone to break only by raising the Young's modulus of the bonding material layer.